1. Field of the Invention:
The invention relates to a television installation comprising a circuit arrangement for the amplification variation of the video signal in dependence upon its mean value. The installation includes a television camera and a monitor. A circuit of this type serves the purpose of control of the amplification of the video signal in order that the brightness on the monitor exhibits a constant or uniform distribution.
2. Description of the Prior Art:
In German AS No. 20 07 905, incorporated herein by reference, a television installation of the cited type is described in which there is connected after an output of the television camera an amplification control circuit which alters the amplification of the video signal of the television camera. For this purpose, the video signal is removed from a following amplifier and supplied to a circuit for the generation of a control signal which acts on the amplification control circuit for the purpose of influencing the amplification.
In the case of television systems, in particular in the case of X-ray television systems, amplitude variations of the image signal frequently occur. They are based e.g. on a chronological variation of the X-ray dose, on mains voltage variations, on non-constant time behavior of the switching members of the high voltage generator, or on a rising or changing characteristic behavior of the television pickup tube. The amplification control adjustment installed in these television systems cannot prevent the brief picture signal variations since the latter require at least the time of one image or picture period (one vertical frame, for example) for the measured value detection. In addition, the response times of control units and final control elements have a disadvantageous and time-delaying effect on the control adjustment.